This invention relates generally to apparatus and methods for measuring liquid levels in a tank or any liquid/liquid or liquid/gas interface. More particularly, this invention relates to a fiber optic device for measuring liquid levels. Still more particularly, this invention relates to a fiber optic device for measuring liquid levels with accuracy suitable for detecting the existence of slow leaks theft, evaporation or environmentally induced changes in liquid levels.
Current techniques for measuring liquid levels in both underground and surface mounted tanks have the deficiencies of excessive complexity and cost or lack the intrinsic safety required for use with volatile liquids or liquids in explosive atmospheres.
There are substantial difficulties involved in making an accurate measurement of the amount of liquid contained in a bulk storage tank. Such tanks may be underground or have opaque walls, which prevents any direct visual inspection of the liquid depth. Typically liquid depths in bulk storage tanks are measured by inserting a long wooden pole into the tank and measuring the depth to which the liquid rose on the pole. This method is inherently inaccurate so that it is possible for a tank to leak part of the contents into the ground for a considerable time without the leak being noticed.
Great care must be exercised in measuring the depth of a liquid such as gasoline because of the risk of fire or explosion. The volatility of many liquids precludes the use of electrical depth measuring apparatus unless equipped with elaborate safety barriers. There is a need for an accurate technique for measuring fluid depths without increasing the risk of fire or explosion.